Obama's lead shrinks again

UPDATED & BUMPED: L.A. Times:

Overall, Obama holds a narrow edge over the Arizona senator, 45% to 43%, which falls within the poll's margin of sampling error of plus or minus 3 percentage points. In June, Obama was ahead by 12 points. Other polls at that time showed him with a narrower lead.More striking than the head-to-head matchup, however, is the drop in Obama's favorable rating in the run-up to his selection of a running mate and the Democratic National Convention next week in Denver.
Obama's favorable rating has sunk to 48% from 59% since the last Times/Bloomberg poll in June. At the same time, his negative rating has risen to 35% from 27%.

PREVIOUSLY:
Gallup: Obama 45%, McCain 44%
Rasmussen: Obama 47%, McCain 45%
Quinnipiac: Obama 47%, McCain 42%

Relatively minor shifts in tracking numbers from day to day don't mean much -- "statistical noise" -- but by measuring at longer periods, trends emerge. If you look at the Gallup chart, you see that Obama's average lead has been 1 point over the past five days (Aug. 14-18), whereas during the previous five days (Aug. 9-13) Obama's average lead was 4.4 points.

Extend the Gallup timeline farther back, and you see the race previously tightened to a dead heat July 30-Aug. 2, after Obama's European trip began with a big bounce that saw him average a 7.2-point lead during the 5-day period July 24-28. That earlier bounce peaked at a 9-point lead for Obama July 26, whereas his most recent bounce peaked at a 6-point lead Aug. 12.

As the campaign wears on, Obama's upward bounces seem to be shrinking, and McCain's numbers are slightly improving. Since McCain brought in Rove protege Steve Schmidt and went over on the attack, this has increased negative perceptions of Obama among independents and "soft" Democratic-leaning voters. So when Obama has a good week, his numbers don't bounce up near 50% quite as easily as they did in July.

Everybody says they had negative campaigns and "attack" ads, but let's face it: That stuff works. In the past 10 days, the Obama campaign has unleashed a steady stream of attacks on McCain, but Maverick's strong performance at the Saddleback forum is an independent variable that should boost his numbers over the coming week -- at least until Obama gets another poll bounce from his VP announcement and the Democratic convention.

UPDATE: Reinforcing the general trend of a tightening race, six weeks ago, Quinnipiac had Obama +9 -- 50% to McCain's 41% -- compared to their latest national poll at +5.